Storage Modes for Tiltrotor Aircraft

ABSTRACT

A tiltrotor aircraft having a VTOL flight mode, a forward flight mode and a storage mode includes a fuselage having a wing rotatably mounted thereto. The wing has an orientation generally perpendicular to the fuselage, in the flight modes, and an orientation generally parallel to the fuselage, in the storage mode. First and second pylon assemblies are positioned proximate outboard ends of the wing. First and second mast assemblies are respectively rotatable relative to the first and second pylon assemblies and have generally vertical orientations, in the VTOL flight mode, and generally horizontal orientations, in the forward flight mode and the storage mode. First and second proprotor assemblies are respectively rotatable relative to the first and second mast assemblies. Each proprotor assembly includes a plurality of rotor blades and has a radially extended orientation, in the flight modes, and a stowed orientation, in the storage mode.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates, in general, to tiltrotor aircraft havinga VTOL flight mode, a forward flight mode and a storage mode and, inparticular, to systems and method of stowing the rotor blades and thewing of a tiltrotor aircraft to reduced the footprint of the tiltrotoraircraft in the storage mode.

BACKGROUND

Fixed-wing aircraft, such as airplanes, are capable of flight usingwings that generate lift responsive to the forward airspeed of theaircraft, which is generated by thrust from one or more jet engines orpropellers. The wings generally have an airfoil cross section thatdeflects air downward as the aircraft moves forward, generating the liftforce to support the aircraft in flight. Fixed-wing aircraft, however,typically require a runway that is hundreds or thousands of feet longfor takeoff and landing.

Unlike fixed-wing aircraft, vertical takeoff and landing (VTOL) aircraftdo not require runways. Instead, VTOL aircraft are capable of takingoff, hovering and landing vertically. One example of a VTOL aircraft isa helicopter which is a rotorcraft having one or more rotors thatprovide lift and thrust to the aircraft. The rotors not only enablehovering and vertical takeoff and landing, but also enable forward,backward and lateral flight. These attributes make helicopters highlyversatile for use in congested, isolated or remote areas. Helicopters,however, typically lack the forward airspeed of fixed-wing aircraft dueto the phenomena of retreating blade stall and advancing bladecompression.

Tiltrotor aircraft attempt to overcome this drawback by including a setof proprotors that can change their plane of rotation based on theoperation being performed. Tiltrotor aircraft generate lift andpropulsion using proprotors that are typically coupled to nacellesmounted near the ends of a fixed wing. The nacelles rotate relative tothe fixed wing such that the proprotors have a generally horizontalplane of rotation in a VTOL flight mode and a generally vertical planeof rotation while cruising in a forward flight mode, wherein the fixedwing provides lift and the proprotors provide forward thrust. In thismanner, tiltrotor aircraft combine the vertical lift capability of ahelicopter with the speed and range of fixed-wing aircraft.

It has been found, however, that tiltrotor aircraft may occupy a largefootprint when not in use, such as during storage on an aircraft carrierflight deck. Accordingly, certain tiltrotor aircraft are operable toperform a conversion from flight mode to storage mode, as seen in priorart FIGS. 1A-1D. In FIG. 1A, a tiltrotor aircraft is shown in VTOLflight mode with the nacelles positioned in a generally verticalorientation and with the proprotors operable for rotation in a generallyhorizontal plane. In FIG. 1B, two of the rotor blades of each proprotorhave been folded in the beamwise direction such that all blades aregenerally parallel to the wing. In FIG. 1C, the nacelles have beenrotated approximately ninety degrees relative to the wing to a generallyhorizontal orientation. In FIG. 1D, the wing has been rotatedapproximately ninety degrees relative to the fuselage of the tiltrotoraircraft such that the wing is generally parallel with the fuselage. Inthe illustrated storage mode of the tiltrotor aircraft, its footprinthas been minimized. It has been found, however, that storing a tiltrotoraircraft with the rotor blades fully cantilevered to one side of thedrive system results in an undesirably large moment being placed on thedrive system, which may cause damage to bearings or other components ofthe drive system. Accordingly, a need has arisen for improved storagemodes for tiltrotor aircraft.

SUMMARY

In a first aspect, the present disclosure is directed to a tiltrotoraircraft having a VTOL flight mode, a forward flight mode and a storagemode. The aircraft includes a fuselage and a wing rotatably mounted tothe fuselage and having first and second outboard ends. The wing isreversibly rotatable between a flight orientation, generallyperpendicular to the fuselage, in the flight modes, and a stowedorientation, generally parallel to the fuselage, in the storage mode.First and second pylon assemblies are respectively positioned proximatethe first and second outboard ends of the wing. First and second mastassemblies are respectively rotatable relative to the first and secondpylon assemblies. The first and second mast assemblies are reversiblyrotatable between a generally vertical orientation, in the VTOL flightmode, and a generally horizontal orientation, in the forward flight modeand the storage mode. First and second proprotor assemblies arerespectively rotatable relative to the first and second mast assemblies.The first and second proprotor assemblies each includes first, secondand third rotor blades and each have a radially extended orientation, inthe flight modes, and a stowed orientation, in the storage mode, whereinthe first rotor blade of each proprotor assembly is folded beamwisebelow the wing generally conforming with the respective pylon assemblyand the second and third rotor blades of each proprotor assembly arefolded beamwise above the wing generally conforming with the respectivepylon assembly.

In some embodiments, first and second tail members may be mounted to thefuselage and may be reversibly rotatable between a dihedral orientation,in the flight modes, and an anhedral orientation, in the storage mode.In certain embodiments, the first proprotor assembly may rotate in phasewith the second proprotor assembly and/or the first and second proprotorassemblies may have matched counter rotation. In some embodiments, eachproprotor assembly may include a rotor hub to which the respective rotorblades are hingeably coupled thereto. In certain embodiments, eachproprotor assembly may include a plurality of rotor blade actuators,such as rotary actuators, that are operable to reversibly rotate therespective rotor blades between the radially extended orientation andthe stowed orientation. In some embodiments, each mast assembly mayinclude a pitch control assembly that is operable to control acollective pitch of the rotor blades of the respective proprotorassembly. In certain embodiments, each pylon assemblies may include aconversion actuator, such as a linear actuator, that is operable toreversibly rotate the respective mast assembly between the generallyvertical orientation and the generally horizontal orientation.

In a second aspect, the present disclosure in directed to a method ofconverting a tiltrotor aircraft from a VTOL flight mode to a storagemode. The aircraft includes a fuselage, a wing rotatably mounted to thefuselage and having first and second outboard ends, first and secondpylon assemblies respectively positioned proximate the first and secondoutboard ends of the wing, first and second mast assemblies respectivelyrotatable relative to the first and second pylon assemblies and firstand second proprotor assemblies respectively rotatable relative to thefirst and second mast assemblies. The method includes rotating the firstand second mast assemblies from a generally vertical orientation to agenerally horizontal orientation; folding a first rotor blade of eachproprotor assembly beamwise from a radially extended orientation to astowed orientation beneath the wing and generally conforming with therespective pylon assembly; folding second and third rotor blades of eachproprotor assembly beamwise from radially extended orientations tostowed orientations above the wing and generally conforming with therespective pylon assembly; and rotating the wing from a flightorientation, generally perpendicular to the fuselage, to a stowedorientation, generally parallel to the fuselage.

The method may also include rotating first and second tail membersmounted to the fuselage from a dihedral orientation to an anhedralorientation; counter rotating the proprotor assemblies, for example 30degrees, during the step of folding the first rotor blade of eachproprotor assembly beamwise from the radially extended orientation tothe stowed orientation and/or collectively adjusting a pitch of therotor blades of each proprotor assembly before the folding steps.

The method may also involve performing at least a portion of the step offolding the first rotor blade of each proprotor assembly beamwise fromthe radially extended orientation to the stowed orientation while thefirst and second mast assemblies are being rotated from the generallyvertical orientation to the generally horizontal orientation; performingat least a portion of the step of folding the second and third rotorblades of each proprotor assembly beamwise from radially extendedorientations to stowed orientations while the first and second mastassemblies are being rotated from the generally vertical orientation tothe generally horizontal orientation; performing at least a portion ofthe step of folding the first rotor blade of each proprotor assemblybeamwise from the radially extended orientation to the stowedorientation while the wing is being rotated from the flight orientation,generally perpendicular to the fuselage, to the stowed orientation,generally parallel to the fuselage; performing at least a portion of thestep of folding the second and third rotor blades of each proprotorassembly beamwise from radially extended orientations to stowedorientations while the wing is being rotated from the flightorientation, generally perpendicular to the fuselage, to the stowedorientation, generally parallel to the fuselage and/or performing atleast a portion of the step of rotating the first and second mastassemblies from the generally vertical orientation to the generallyhorizontal orientation while the wing is being rotated from the flightorientation, generally perpendicular to the fuselage, to the stowedorientation, generally parallel to the fuselage.

In a third aspect, the present disclosure is directed to a tiltrotoraircraft having a VTOL flight mode, a forward flight mode and a storagemode. The aircraft includes a fuselage and a wing rotatably mounted tothe fuselage and having first and second outboard ends. The wing isreversibly rotatable between a flight orientation, generallyperpendicular to the fuselage, in the flight modes, and a stowedorientation, generally parallel to the fuselage, in the storage mode.First and second pylon assemblies are respectively positioned proximatethe first and second outboard ends of the wing. First and second mastassemblies are respectively rotatable relative to the first and secondpylon assemblies. The first and second mast assemblies are reversiblyrotatable between a generally vertical orientation, in the VTOL flightmode, and a generally horizontal orientation, in the forward flight modeand the storage mode. First and second proprotor assemblies arerespectively rotatable relative to the first and second mast assemblies.The first and second proprotor assemblies each includes first, secondand third rotor blades and each have a radially extended orientation, inthe flight modes, and a stowed orientation, in the storage mode, whereinthe first rotor blade of each proprotor assembly is folded chordwisebelow the wing generally conforming with the respective pylon assembly,the second rotor blade of each proprotor assembly is folded chordwiseabove the wing generally conforming with the respective pylon assemblyand the third rotor blade of each proprotor assembly is inboardlyextended generally parallel with the wing.

In some embodiments, each proprotor assembly may include a plurality ofrotor blade locking assemblies that are operable to enable reversiblerotation, such as manual reversible rotation, of the respective rotorblades between the radially extended orientation and the stowedorientation. In certain embodiments, the rotor blade locking assembliesmay be operable to lock the respective rotor blades in the stowedorientation.

In a fourth aspect, the present disclosure in directed to a method ofconverting a tiltrotor aircraft from a VTOL flight mode to a storagemode. The aircraft includes a fuselage, a wing rotatably mounted to thefuselage and having first and second outboard ends, first and secondpylon assemblies respectively positioned proximate the first and secondoutboard ends of the wing, first and second mast assemblies respectivelyrotatable relative to the first and second pylon assemblies and firstand second proprotor assemblies respectively rotatable relative to thefirst and second mast assemblies. The method includes rotating the firstand second mast assemblies from a generally vertical orientation to agenerally horizontal orientation; positioning a first rotor blade ofeach proprotor assembly in a generally upwardly extending verticalorientation; folding a second rotor blade of each proprotor assemblychordwise from a radially extended orientation to an intermediateorientation; positioning a third rotor blade of each proprotor assemblyin a inboardly extending generally parallel with the wing orientation;folding the second rotor blade of each proprotor assembly chordwise fromthe intermediate orientation to a stowed orientation beneath the wingand generally conforming with the respective pylon assembly; folding thefirst rotor blade of each proprotor assembly chordwise from a radiallyextended orientation to a stowed orientation above the wing andgenerally conforming with the respective pylon assembly; and rotatingthe wing from a flight orientation, generally perpendicular to thefuselage, to a stowed orientation, generally parallel to the fuselage.

The method may also include counter rotating the proprotor assembliesbetween the steps of positioning the first rotor blade of each proprotorassembly in the generally upwardly extending vertical orientation andpositioning the third rotor blade of each proprotor assembly in theinboardly extending generally parallel with the wing orientation;feathering the rotor blades of each proprotor assembly before thefolding steps; manually folding the second rotor blade of each proprotorassembly chordwise from the radially extended orientation to theintermediate orientation; manually folding the second rotor blade ofeach proprotor assembly chordwise from the intermediate orientation tothe stowed orientation; manually folding the first rotor blade of eachproprotor assembly chordwise from the radially extended orientation tothe stowed orientation and/or locking the first and second rotor bladesof each proprotor assembly in the stowed orientations.

In a fifth aspect, the present disclosure is directed to a tiltrotoraircraft having a VTOL flight mode, a forward flight mode and a storagemode. The aircraft includes a fuselage and a wing rotatably mounted tothe fuselage and having first and second outboard ends. The wing isreversibly rotatable between a flight orientation, generallyperpendicular to the fuselage, in the flight modes, and a stowedorientation, generally parallel to the fuselage, in the storage mode.First and second pylon assemblies are respectively positioned proximatethe first and second outboard ends of the wing. First and second mastassemblies are respectively rotatable relative to the first and secondpylon assemblies. The first and second mast assemblies are reversiblyrotatable between a generally vertical orientation, in the VTOL flightmode, and a generally horizontal orientation, in the forward flight modeand the storage mode. First and second proprotor assemblies arerespectively rotatable relative to the first and second mast assemblies.The first and second proprotor assemblies each includes first, secondand third rotor blades and each have a radially extended orientation, inthe flight modes, and a stowed orientation, in the storage mode, whereinthe first and second rotor blades of each proprotor assembly are foldedbeamwise to be generally parallel with the respective third rotor blade,the rotor blades of the first proprotor assembly have an ascendingorientation relative to the wing and the rotor blades of the secondproprotor assembly a descending orientation relative to the wing.

In some embodiments, in the storage mode, the first proprotor assemblymay be positioned aft of the second proprotor assembly. In certainembodiments, the ascending orientation of the rotor blades of the firstproprotor assembly relative to the wing may be an angle of approximately30 degrees and the descending orientation of the rotor blades of thesecond proprotor assembly relative to the wing may be an angle ofapproximately 30 degrees. In some embodiments, the first proprotorassembly may rotate approximately 60 degrees out of phase with thesecond proprotor assembly.

In a sixth aspect, the present disclosure in directed to a method ofconverting a tiltrotor aircraft from a VTOL flight mode to a storagemode. The aircraft includes a fuselage, a wing rotatably mounted to thefuselage and having first and second outboard ends, first and secondpylon assemblies respectively positioned proximate the first and secondoutboard ends of the wing, first and second mast assemblies respectivelyrotatable relative to the first and second pylon assemblies and firstand second proprotor assemblies respectively rotatable relative to thefirst and second mast assemblies. The method includes folding first andsecond rotor blades of each proprotor assembly beamwise to be generallyparallel with a respective third rotor blade; rotating the wing from aflight orientation, generally perpendicular to the fuselage, to a stowedorientation, generally parallel to the fuselage; rotating the first andsecond mast assemblies from a generally vertical orientation to agenerally horizontal orientation; and counter rotating the first andsecond proprotor assemblies such that the rotor blades of the firstproprotor assembly have an ascending orientation relative to the wingand the rotor blades of the second proprotor assembly have a descendingorientation relative to the wing.

The method may also include counter rotating the first and secondproprotor assemblies such that the ascending orientation of the rotorblades of the first proprotor assembly relative to the wing may be anangle of approximately 30 degrees and the descending orientation of therotor blades of the second proprotor assembly relative to the wing maybe an angle of approximately 30 degrees and/or positioning the firstproprotor assembly aft of the second proprotor assembly.

The method may also involve performing at least a portion of the step offolding the first and second rotor blades of each proprotor assemblybeamwise to be generally parallel with the respective third rotor bladewhile the first and second proprotor assemblies are being counterrotated; performing at least a portion of the step of folding the firstand second rotor blades of each proprotor assembly beamwise to begenerally parallel with the respective third rotor blade while the wingis being rotated from the flight orientation, generally perpendicular tothe fuselage, to the stowed orientation, generally parallel to thefuselage and/or performing the step of folding the first and secondrotor blades of each proprotor assembly beamwise to be generallyparallel with the respective third rotor blade before rotating the firstand second mast assemblies from the generally vertical orientation tothe generally horizontal orientation.

In a seventh aspect, the present disclosure is directed to a tiltrotoraircraft having a VTOL flight mode, a forward flight mode and a storagemode. The aircraft includes a fuselage and a wing rotatably mounted tothe fuselage and having first and second outboard ends. The wing isreversibly rotatable between a flight orientation, generallyperpendicular to the fuselage, in the flight modes, and a stowedorientation, generally parallel to the fuselage, in the storage mode.First and second pylon assemblies are respectively positioned proximatethe first and second outboard ends of the wing. First and second mastassemblies are respectively rotatable relative to the first and secondpylon assemblies. The first and second mast assemblies are reversiblyrotatable between a generally vertical orientation, in the VTOL flightmode, and a generally horizontal orientation, in the forward flight modeand the storage mode. First and second proprotor assemblies arerespectively rotatable relative to the first and second mast assemblies.The first and second proprotor assemblies each includes first, secondand third rotor blades and each have a radially extended orientation, inthe flight modes, and a stowed orientation, in the storage mode, whereinthe first rotor blade of the first proprotor assembly is folded beamwisebelow the wing generally conforming with the respective pylon assembly,the second and third rotor blades of the first proprotor assembly arefolded beamwise above the wing generally conforming with the respectivepylon assembly, the first and second rotor blades of the secondproprotor assembly are folded beamwise to be generally parallel with thethird rotor blade of the second proprotor assembly and the rotor bladesof the second proprotor assembly have a descending orientation relativeto the wing.

In an eighth aspect, the present disclosure in directed to a method ofconverting a tiltrotor aircraft from a VTOL flight mode to a storagemode. The aircraft includes a fuselage, a wing rotatably mounted to thefuselage and having first and second outboard ends, first and secondpylon assemblies respectively positioned proximate the first and secondoutboard ends of the wing, first and second mast assemblies respectivelyrotatable relative to the first and second pylon assemblies and firstand second proprotor assemblies respectively rotatable relative to thefirst and second mast assemblies. The method includes rotating the firstand second mast assemblies from a generally vertical orientation to agenerally horizontal orientation; folding a first rotor blade of thefirst proprotor assembly beamwise from a radially extended orientationto a stowed orientation beneath the wing and generally conforming withthe respective pylon assembly; folding second and third rotor blades ofthe first proprotor assembly beamwise from radially extendedorientations to stowed orientations above the wing and generallyconforming with the respective pylon assembly; folding first and secondrotor blades of the second proprotor assembly beamwise to be generallyparallel with a third rotor blade of the second proprotor assembly;rotating the wing from a flight orientation, generally perpendicular tothe fuselage, to a stowed orientation, generally parallel to thefuselage; and counter rotating the first and second proprotor assembliessuch that the rotor blades of the second proprotor assembly have adescending orientation relative to the wing.

The method may also involve performing at least a portion of the step offolding the first rotor blade of the first proprotor assembly beamwisefrom the radially extended orientation to the stowed orientation whilethe first mast assemblies is being rotated from the generally verticalorientation to the generally horizontal orientation; performing the stepof rotating the first mast assembly from the generally verticalorientation to the generally horizontal orientation before rotating thesecond mast assembly from the generally vertical orientation to thegenerally horizontal orientation; performing at least a portion of thestep of rotating the second mast assembly from the generally verticalorientation to the generally horizontal orientation while the wing isbeing rotated from the flight orientation, generally perpendicular tothe fuselage, to the stowed orientation, generally parallel to thefuselage and/or performing the step of folding the first and secondrotor blades of the second proprotor assembly beamwise to be generallyparallel with the respective third rotor blade before rotating thesecond mast assembly from the generally vertical orientation to thegenerally horizontal orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent disclosure, reference is now made to the detailed descriptionalong with the accompanying figures in which corresponding numerals inthe different figures refer to corresponding parts and in which:

FIGS. 1A-1D are prior art drawings depicting a tiltrotor aircrafttransitioning from a VTOL flight mode to a storage mode;

FIGS. 2A-2B are schematic illustrations of an exemplary tiltrotoraircraft in forward flight mode and in VTOL flight mode in accordancewith embodiments of the present disclosure;

FIG. 3A is an isometric view of an exemplary propulsion system for atiltrotor aircraft in accordance with embodiments of the presentdisclosure;

FIG. 3B is a top view of an exemplary wing section of a tiltrotoraircraft in accordance with embodiments of the present disclosure;

FIGS. 4A-4F are schematic illustrations of an exemplary tiltrotoraircraft transitioning between VTOL flight mode and storage mode inaccordance with embodiments of the present disclosure;

FIGS. 5A-5B are schematic illustrations of an actuation assemblyoperating a rotor blade between a radially extended orientation and astowed orientation in accordance with embodiments of the presentdisclosure;

FIGS. 6A-6F are schematic illustrations of an exemplary tiltrotoraircraft transitioning between VTOL flight mode and storage mode inaccordance with embodiments of the present disclosure;

FIGS. 7A-7B are schematic illustrations of a rotor blade in a radiallyextended orientation and a stowed orientation in accordance withembodiments of the present disclosure;

FIG. 8 is an exploded view of a rotor blade hinging and locking assemblyfor manually operating a rotor blade between a radially extendedorientation and a stowed orientation in accordance with embodiments ofthe present disclosure;

FIGS. 9A-9D are top views of a rotor blade hinging and locking assemblyfor manually operating a rotor blade between a radially extendedorientation and a stowed orientation in accordance with embodiments ofthe present disclosure;

FIGS. 10A-10D are side views of a rotor blade hinging and lockingassembly for manually operating a rotor blade between a radiallyextended orientation and a stowed orientation in accordance withembodiments of the present disclosure;

FIGS. 11A-11B are schematic illustrations of an exemplary tiltrotoraircraft in forward flight mode and in VTOL flight mode in accordancewith embodiments of the present disclosure;

FIGS. 12A-12F are schematic illustrations of an exemplary tiltrotoraircraft transitioning between VTOL flight mode and storage mode inaccordance with embodiments of the present disclosure; and

FIGS. 13A-13F are schematic illustrations of an exemplary tiltrotoraircraft transitioning between VTOL flight mode and storage mode inaccordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

While the making and using of various embodiments of the presentdisclosure are discussed in detail below, it should be appreciated thatthe present disclosure provides many applicable inventive concepts,which can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed herein are merely illustrative and do notdelimit the scope of the present disclosure. In the interest of clarity,not all features of an actual implementation may be described in thisspecification. It will of course be appreciated that in the developmentof any such actual embodiment, numerous implementation-specificdecisions must be made to achieve the developer's specific goals, suchas compliance with system-related and business-related constraints,which will vary from one implementation to another. Moreover, it will beappreciated that such a development effort might be complex andtime-consuming but would be a routine undertaking for those of ordinaryskill in the art having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present disclosure, the devices,members, apparatuses, and the like described herein may be positioned inany desired orientation. Thus, the use of terms such as “above,”“below,” “upper,” “lower” or other like terms to describe a spatialrelationship between various components or to describe the spatialorientation of aspects of such components should be understood todescribe a relative relationship between the components or a spatialorientation of aspects of such components, respectively, as the devicedescribed herein may be oriented in any desired direction.

Referring to FIGS. 2A-2B in the drawings, a tiltrotor aircraft isschematically illustrated and generally designated 10. Aircraft 10includes a fuselage 12, a wing mount assembly 14 that is rotatablerelative to fuselage 12 and a tail assembly 16 including rotatablymounted tail members 16 a, 16 b having control surfaces operable forhorizontal and/or vertical stabilization during forward flight. A wingmember 18 is supported by wing mount assembly 14 and rotates with wingmount assembly 14 relative to fuselage 12 as discussed herein. Locatedat outboard ends of wing member 18 are propulsion assemblies 20 a, 20 b.Propulsion assembly 20 a includes a nacelle depicted as fixed pylon 22 athat houses an engine and transmission. In addition, propulsion assembly20 a includes a mast assembly 24 a that is rotatable relative to fixedpylon 22 a between a generally horizontal orientation, as best seen inFIG. 2A, a generally vertical orientation, as best seen in FIG. 2B.Propulsion assembly 20 a also includes a proprotor assembly 26 a that isrotatable relative to mast assembly 24 a responsive to torque androtational energy provided via a rotor hub assembly and drive systemmechanically coupled to the engine and transmission. Likewise,propulsion assembly 20 b includes a nacelle depicted as fixed pylon 22 bthat houses an engine and transmission, a mast assembly 24 b that isrotatable relative to fixed pylon 22 b and a proprotor assembly 26 bthat is rotatable relative to mast assembly 24 b responsive to torqueand rotational energy provided via a rotor hub assembly and drive systemmechanically coupled to the engine and transmission.

FIG. 2A illustrates aircraft 10 in airplane or forward flight mode, inwhich proprotor assemblies 26 a, 26 b are rotating in a substantiallyvertical plane to provide a forward thrust enabling wing member 18 toprovide a lifting force responsive to forward airspeed, such thataircraft 10 flies much like a conventional propeller driven aircraft.FIG. 2B illustrates aircraft 10 in helicopter or VTOL flight mode, inwhich proprotor assemblies 26 a, 26 b are rotating in a substantiallyhorizontal plane to provide a lifting thrust, such that aircraft 10flies much like a conventional helicopter. It should be appreciated thataircraft 10 can be operated such that proprotor assemblies 26 a, 26 bare selectively positioned between forward flight mode and VTOL flightmode, which can be referred to as a conversion flight mode. Even thoughaircraft 10 has been described as having one engine in each fixed pylon22 a, 22 b, it should be understood by those having ordinary skill inthe art that other engine arrangements are possible and are consideredto be within the scope of the present disclosure including, for example,having a single engine which may be housed within the fuselage thatprovides torque and rotational energy to both proprotor assemblies 26 a,26 b.

In the illustrated embodiment, proprotor assemblies 26 a, 26 b eachinclude three twisted rotor blades that are equally spaced apartcircumferentially at approximately 120 degree intervals. It should beunderstood by those having ordinary skill in the art, however, thatproprotor assemblies 26 a, 26 b of the present disclosure could haverotor blades with other designs and other configurations. During flightmodes, proprotor assemblies 26 a, 26 b rotate in opposite directions toprovide torque balancing to aircraft 10. For example, when viewed fromthe front of aircraft 10 in forward flight mode, proprotor assembly 26 arotates clockwise and proprotor assembly 26 b rotates counterclockwise.In addition, proprotor assemblies 26 a, 26 b rotate in phase with eachother such that the rotor blades of each proprotor assembly 26 a, 26 bpass wing member 18 at the same time during all modes of operation ofaircraft 10. Further, as discussed herein, proprotor assemblies 26 a, 26b are mechanically coupled to a common interconnect drive shaft suchthat proprotor assemblies 26 a, 26 b have matched counter rotationwherein any rotation of one proprotor assembly 26 a, 26 b results in anequal counter rotation of the other of proprotor assembly 26 a, 26 b.

Referring now to FIGS. 3A-3B, propulsion assembly 20 a is disclosed infurther detail. Propulsion assembly 20 a is substantially similar topropulsion assembly 20 b therefore, for sake of efficiency, certainfeatures will be disclosed only with regard to propulsion assembly 20 a.One having ordinary skill in the art, however, will fully appreciate anunderstanding of propulsion assembly 20 b based upon the disclosureherein of propulsion assembly 20 a. Propulsion assembly 20 a includes anengine 30 that is fixed relative to wing 18. An engine output shaft 32transfers power from engine 30 to a spiral bevel gearbox 34 thatincludes spiral bevel gears to change torque direction by 90 degreesfrom engine 30 to a fixed gearbox 36 via a clutch. Fixed gearbox 36includes a plurality of gears, such as helical gears, in a gear trainthat are coupled to an interconnect drive shaft 38 and a quill shaft(not visible) that supplies torque to an input in spindle gearbox 40 ofproprotor gearbox 42.

Interconnect drive shaft 38 provides a torque path that enables a singleengine of aircraft 10 to provide torque to both proprotors 26 a, 26 b inthe event of a failure of the other engine. In the illustratedembodiment, interconnect drive shaft 38 has a rotational axis 44 that isaft of a conversion axis 46 of spindle gearbox 40. Conversion axis 46 isparallel to a lengthwise axis 48 of wing 18. In the illustratedembodiment, interconnect drive shaft 38 includes a plurality of segmentsthat share common rotational axis 44. The location of interconnect driveshaft 38 aft of wing spar 50 provides for optimal integration with fixedgearbox 36 without interfering with the primary torque transfer in thequill shaft between fixed gearbox 36 and spindle gearbox 40.

Engine 30 is housed and supported in fixed pylon 22 a (see FIGS. 2A-2B)that may include features such as an inlet, aerodynamic fairings andexhaust, as well as other structures and systems to support andfacilitate the operation of engine 30. Proprotor 26 a of propulsionassembly 20 a includes three rotor blades 52 a, 52 b, 52 c that arehingeably coupled to grip assemblies of a rotor hub 54. Rotor hub 54 iscoupled to a mast 56 that is coupled to proprotor gearbox 42. Together,spindle gearbox 40, proprotor gearbox 42 and mast 56 are part of mastassembly 24 a that rotates relative to fixed pylon 22 a. In addition, itshould be appreciated by those having ordinary skill in the art thatmast assembly 24 a may include different or additional components, suchas a pitch control assembly depicted as swashplate 58, actuators 60 andpitch links 62, wherein swashplate 58 is selectively actuated byactuators 60 to selectively control the collective pitch and the cyclicpitch of rotor blades 52 a, 52 b, 52 c via pitch links 62. A linearactuator, depicted as conversion actuator 64 of fixed pylon 22 a, isoperable to reversibly rotate mast assembly 24 a relative to fixed pylon22 a, which in turn selectively positions proprotor assembly 26 abetween forward flight mode, in which proprotor assembly 26 a isrotating in a substantially vertical plane, and VTOL flight mode, inwhich proprotor assembly 26 a is rotating in a substantially horizontalplane.

Referring next to FIGS. 4A-4F of the drawings, tiltrotor aircraft 10 isdepicted in various states during a transition between VTOL flight modeand storage mode. Aircraft 10 has a VTOL flight mode, as best seen inFIG. 2B, a forward flight mode, as best seen in FIG. 2A, and a storagemode, as best seen in FIG. 4F. As discussed above, aircraft 10 includesfuselage 12 and wing 18 that is rotatably mounted to fuselage 12. Wing18 is reversibly rotatable between a flight orientation that isgenerally perpendicular to fuselage 12, as best seen in FIG. 4A, and astowed orientation that is generally parallel to fuselage 12, as bestseen in FIG. 4F. Pylon assemblies 22 a, 22 b are positioned proximatethe outboard ends of wing 18. Mast assemblies 24 a, 24 b arerespectively rotatable relative to pylon assemblies 22 a, 22 b. Mastassemblies 24 a, 24 b are reversibly rotatable between a generallyvertical orientation, as best seen in FIG. 4A, and a generallyhorizontal orientation, as best seen in FIG. 4F. Proprotor assemblies 26a, 26 b are respectively rotatable relative to mast assemblies 24 a, 24b. Proprotor assembly 26 a includes rotor blades 52 a, 52 b, 52 c andproprotor assembly 26 b includes rotor blades 52 d, 52 e, 52 f.Proprotor assemblies 26 a, 26 b each have a radially extendedorientation, as best seen in FIG. 4A, and a stowed orientation, as bestseen in FIG. 4F. More specifically in the stowed orientation, rotorblade 52 a of proprotor assembly 26 a is folded beamwise below wing 18and generally conforming with pylon assembly 22 a and rotor blade 52 dof proprotor assembly 26 b is folded beamwise below wing 18 andgenerally conforming with pylon assembly 22 b. Rotor blades 52 b, 52 cof proprotor assembly 26 a are folded beamwise above wing 18 andgenerally conforming with pylon assembly 22 a and rotor blades 52 e, 52f of proprotor assembly 26 b are folded beamwise above wing 18 andgenerally conforming with pylon assembly 22 b.

An example conversion operation of aircraft 10 from VTOL flight mode tostorage mode will now be described. During conversion processes, it isimportant to avoid contact between the various components of aircraft 10with each other as well as to avoid contact between the variouscomponents of aircraft 10 and the surface on which aircraft 10 rests. Toachieve this result, certain of the conversion steps, or portionsthereof, may need to be performed before or while other steps, orportions thereof, are being performed. These sequential and/orsimultaneous operations are enabled by having individually controlledactuators operating to transition the various components of aircraft 10independent of one another. For example, rotation of wing 18 relative tofuselage 12 is independent of rotation of mast assembly 24 a relative topylon assembly 22 a. Likewise, rotation of mast assembly 24 a relativeto pylon assembly 22 a is independent of rotation mast assembly 24 brelative to pylon assembly 22 b. Similarly, rotation of mast assembly 24a relative to pylon assembly 22 a is independent of rotation of rotorblades 52 a, 52 b, 52 c relative to rotor hub 54. In addition, rotationof rotor blade 52 a relative to rotor hub 54 is independent of rotationof rotor blade 52 b and independent of rotation of rotor blade 52 crelative to rotor hub 54. As such, those having ordinary skill in theart will understand that all such operations may be controlledindividually and independent of one another. Accordingly, the order ofoperations and sequencing thereof may take a variety of forms, each ofwhich is considered to be within the scope of the present disclosure.

In FIG. 4A, aircraft 10 is best characterized as being in VTOL flightmode. As illustrated, wing 18 is in flight orientation, generallyperpendicular to fuselage 12. Mast assemblies 24 a, 24 b are each in agenerally vertical orientation. Proprotor assemblies 26 a, 26 b are eachin a radially extended orientation. Tail members 16 a, 16 b are in adihedral orientation. Rotor blades 52 a, 52 b, 52 c have beencollectively operated to have a generally horizontal orientation. Rotorblades 52 d, 52 e, 52 f have been collectively operated to have agenerally horizontal orientation. In FIG. 4B, the conversion from VTOLflight mode to storage mode has begun. As illustrated, wing 18 remainsin flight orientation, generally perpendicular to fuselage 12. Mastassemblies 24 a, 24 b have rotated approximately 30 degrees from thevertical orientation toward the horizontal orientation. Tail members 16a, 16 b have begun to lower. Rotor blades 52 a, 52 b have begun to foldbeamwise, while rotor blade 52 c remains radially extended. Rotor blades52 d, 52 e have begun to fold beamwise, while rotor blade 52 f remainsradially extended.

In FIG. 4C, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 18 remains in flight orientation,generally perpendicular to fuselage 12. Mast assemblies 24 a, 24 b haverotated approximately 45 degrees from the vertical orientation towardthe horizontal orientation. Tail members 16 a, 16 b continue to lower.Rotor blades 52 a, 52 bcontinue to fold, while rotor blade 52 c remainsradially extended. Rotor blades 52 d, 52 e continue to fold, while rotorblade 52 f remains radially extended. Proprotor assemblies 26 a, 26 bhave counter rotated approximately 30 degrees such that rotor blades 52c, 52 f are inboardly extended generally parallel with wing 18. Rotorblades 52 a, 52 d have cleared pylon assemblies 22 a, 22 b and aregenerally vertical having sufficient ground clearance to continuefolding. In FIG. 4D, the conversion from VTOL flight mode to storagemode continues. As illustrated, wing 18 remains in flight orientation,generally perpendicular to fuselage 12. Mast assemblies 24 a, 24 b haverotated approximately 60 degrees from the vertical orientation towardthe horizontal orientation. Tail members 16 a, 16 b continue to lower.Rotor blades 52 a, 52 b continue to fold, while rotor blade 52 c remainsradially extended until sufficient clearance with wing 18 is establishedallowing rotor blade 52 c to begin beamwise folding. Rotor blades 52 d,52 e continue to fold, while rotor blade 52 f remains radially extendeduntil sufficient clearance with wing 18 is established allowing rotorblade 52 f to begin beamwise folding.

In FIG. 4E, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 18 has rotated approximately 45 degreesrelative to fuselage 12. Mast assemblies 24 a, 24 b have rotated to thehorizontal orientation. Tail members 16 a, 16 b are fully lowered to ananhedral orientation. Rotor blade 52 a is in a stowed orientationbeneath wing 18 and generally conforming with pylon assembly 22 a. Rotorblades 52 b, 52 c are each in a stowed orientation above wing 18 andgenerally conforming with pylon assembly 22 a. Rotor blade 52 d is in astowed orientation beneath wing 18 and generally conforming with pylonassembly 22 b. Rotor blades 52 e, 52 f are each in a stowed orientationabove wing 18 and generally conforming with pylon assembly 22 b. In FIG.4F, the conversion from VTOL flight mode to storage mode is complete. Asillustrated, wing 18 is in stowed orientation, generally parallel tofuselage 12. Mast assemblies 24 a, 24 b are in the horizontalorientation. Tail members 16 a, 16 b are fully lowered to the anhedralorientation. Rotor blade 52 a is in a stowed orientation beneath wing 18and generally conforming with pylon assembly 22 a. Rotor blades 52 b, 52c are each in a stowed orientation above wing 18 and generallyconforming with pylon assembly 22 a. Rotor blade 52 d is in a stowedorientation beneath wing 18 and generally conforming with pylon assembly22 b. Rotor blades 52 e, 52 f are each in a stowed orientation abovewing 18 and generally conforming with pylon assembly 22 b.

As illustrated, the storage mode of aircraft 10 depicted and describedwith reference to FIGS. 4A-4F significantly reduces the footprint ofaircraft 10 as compared to the flight modes of aircraft 10. In theillustrated storage mode of aircraft 10, the stowed orientation of therotor blades does not result in an undesirably large moment being placedon the drive systems. To return aircraft 10 from storage mode to VTOLflight mode, a reverse sequence may be followed to avoid contact betweenthe various components of aircraft 10 with each other as well as toavoid contact between the various components of aircraft 10 and thesurface on which aircraft 10 rests.

Referring to FIGS. 5A-5B of the drawings, the beamwise folding operationof a rotor blade is more fully described. The hingeable relationship ofrotor blade 52 a to rotor hub 54 is substantially similar to thehingeable relationship between each rotor blade and the respective rotorhub therefore, for sake of efficiency, certain features will bedisclosed only with regard to rotor blade 52 a and rotor hub 54. Onehaving ordinary skill in the art, however, will fully appreciate anunderstanding of the hingeable relationship between other rotor bladesand rotor hubs based upon the disclosure herein of rotor blade 52 a androtor hub 54. In the illustrated embodiment, rotor blade 52 a isrotatably mounted to a grip assembly 70 of rotor hub 54 by a pair ofspaced blade tangs 72 a, 72 b and a blade pivot pin 74, which extendstherethrough. Mounted within pivot pin 74 is a drive motor 76 that hasplanetary gear reducers 78 a, 78 b mounted on each end thereof. Gearreducer 78 a has an output that is coupled to blade tang 72 a and gearreducer 78 b has an output that is coupled to blade tang 72 b such thatrotor blade 52 a moves responsive to operation of drive motor 76. Asillustrated, drive motor 76 and gear reducers 78 a, 78 b form anactuation assembly depicted as rotary actuator 80 for rotating rotorblade 52 a about axis of rotation 82. In one implementation, drive motor76 reversibly operates to enable rotor blade 52 a to be folded from theradially extended orientation to the stowed orientation and to beunfolded from the stowed orientation to the radially extendedorientation. Preferably, rotor blade 52 a may be locked in the radiallyextended orientation and in the stowed orientation by rotary actuator 80and/or additional locking mechanisms (not shown).

Referring next to FIGS. 6A-6F of the drawings, tiltrotor aircraft 10 isdepicted in various states during a transition between VTOL flight modeand storage mode. Aircraft 10 has a VTOL flight mode, as best seen inFIG. 2B, a forward flight mode, as best seen in FIG. 2A, and a storagemode, as best seen in FIG. 6F. As discussed above, aircraft 10 includesfuselage 12 and wing 18 that is rotatably mounted to fuselage 12. Wing18 is reversibly rotatable between a flight orientation that isgenerally perpendicular to fuselage 12, as best seen in FIG. 6A, and astowed orientation that is generally parallel to fuselage 12, as bestseen in FIG. 6F. Pylon assemblies 22 a, 22 b are positioned proximatethe outboard ends of wing 18. Mast assemblies 24 a, 24 b arerespectively rotatable relative to pylon assemblies 22 a, 22 b. Mastassemblies 24 a, 24 b are reversibly rotatable between a generallyvertical orientation, as best seen in FIG. 6A, and a generallyhorizontal orientation, as best seen in FIGS. 6B-6F. Proprotorassemblies 90 a, 90 b are respectively rotatable relative to mastassemblies 24 a, 24 b. Proprotor assembly 90 aincludes rotor blades 92a, 92 b, 92 c and proprotor assembly 90 b includes rotor blades 92 d, 92e, 92 f. Proprotor assemblies 90 a, 90 b each have a radially extendedorientation, as best seen in FIG. 6A, and a stowed orientation, as bestseen in FIG. 6F. More specifically in the stowed orientation, rotorblade 92 a of proprotor assembly 90 a is folded chordwise below wing 18and generally conforming with pylon assembly 22 a and rotor blade 92 dof proprotor assembly 90 b is folded chordwise below wing 18 andgenerally conforming with pylon assembly 22 b. Rotor blade 92 b ofproprotor 90 a is folded chordwise above wing 18 and generallyconforming with pylon assembly 22 a and rotor blade 92 e of proprotor 90b is folded chordwise above wing 18 and generally conforming with pylonassembly 22 b. Rotor blade 92 c of proprotor 90 a is inboardly extendedgenerally parallel with wing 18 and rotor blade 92 f of proprotor 90 bis inboardly extended generally parallel with wing 18.

An example conversion operation of aircraft 10 from VTOL flight mode tostorage mode will now be described, wherein folding of the rotor bladesis preferably accomplished using a manual process. In FIG. 6A, aircraft10 is best characterized as being in VTOL flight mode. As illustrated,wing 18 is in flight orientation, generally perpendicular to fuselage12. Mast assemblies 24 a, 24 b are each in a generally verticalorientation. Proprotor assemblies 90 a, 90 b are each in a radiallyextended orientation. Tail members 16 a, 16 b are in a dihedralorientation. Rotor blades 92 a, 92 b, 92 c have been collectivelyoperated to have a generally vertical or feathered orientation. Rotorblades 92 d, 92 e, 92 f have been collectively operated to have agenerally vertical or feathered orientation. In FIG. 6B, the conversionfrom VTOL flight mode to storage mode has begun. As illustrated, wing 18remains in flight orientation, generally perpendicular to fuselage 12.Mast assemblies 24 a, 24 b have rotated approximately 90 degrees to thehorizontal orientation. Tail members 16 a, 16 b remains in the dihedralorientation. Rotor blades 92 a, 92 b, 92 c remain radially extended.Rotor blades 92 d, 92 e, 92 f remains radially extended. Proprotorassemblies 90 a, 90 b are positioned such that rotor blade 92 b androtor blade 92 e each has a generally upwardly extending verticalorientation.

In FIG. 6C, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 18 remains in flight orientation,generally perpendicular to fuselage 12. Mast assemblies 24 a, 24 b arein the horizontal orientation. Tail members 16 a, 16 b remains in thedihedral orientation. Rotor blades 92 a, 92 d have been manuallyunlocked and partially folded to manually maintain ground clearance andclearance with pylon assemblies 22 a, 22 b. Rotor blades 92 b, 92 c, 92e, 92 f remain radially extended. In FIG. 6D, the conversion from VTOLflight mode to storage mode continues. As illustrated, wing 18 remainsin flight orientation, generally perpendicular to fuselage 12. Mastassemblies 24 a, 24 b are in the horizontal orientation. Tail members 16a, 16 b remains in the dihedral orientation. Proprotor assemblies 90 a,90 b have counter rotated approximately 30 degrees such that rotorblades 92 c, 92 f are inboardly extending generally parallel with wing18. Rotor blades 92 a, 92 d are now clear of pylon assemblies 22 a, 22 band are folded and locked in a stowed orientation. Rotor blades 92 b, 92c, 92 e, 92 f remain radially extended.

In FIG. 6E, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 18 remains in flight orientation,generally perpendicular to fuselage 12. Mast assemblies 24 a, 24 b arein the horizontal orientation. Tail members 16 a, 16 b remains in thedihedral orientation. Rotor blade 92 a is in a stowed orientationbeneath wing 18 and generally conforming with pylon assembly 22 a. Rotorblade 92 d is in a stowed orientation beneath wing 18 and generallyconforming with pylon assembly 22 b. Rotor blade 92 b has been manuallyunlocked, folded and locked in a stowed orientation above wing 18 andgenerally conforming with pylon assembly 22 a. Rotor blade 92 e has beenmanually unlocked, folded and locked in a stowed orientation above wing18 and generally conforming with pylon assembly 22 b. Rotor blades 92 c,92 f are each inboardly extending generally parallel with wing 18. InFIG. 6F, the conversion from VTOL flight mode to storage mode iscomplete. As illustrated, wing 18 has been rotated approximately 90degrees to a stowed orientation, generally parallel to fuselage 12. Mastassemblies 24 a, 24 b are in the horizontal orientation. Tail members 16a, 16 b are fully lowered to an anhedral orientation. Rotor blade 92 ais in a stowed orientation beneath wing 18 and generally conforming withpylon assembly 22 a. Rotor blade 92 d is in a stowed orientation beneathwing 18 and generally conforming with pylon assembly 22 b. Rotor blade92 b is in a stowed orientation above wing 18 and generally conformingwith pylon assembly 22 a. Rotor blade 92 e is in a stowed orientationabove wing 18 and generally conforming with pylon assembly 22 b. Rotorblades 92 c, 92 f are each inboardly extending generally parallel withwing 18 in a stowed orientation.

As illustrated, the storage mode of aircraft 10 depicted and describedwith reference to FIGS. 6A-6F significantly reduces the footprint ofaircraft 10 as compared to the flight modes of aircraft 10. In theillustrated storage mode of aircraft 10, the stowed orientation of therotor blades does not result in an undesirably large moment being placedon the drive systems. To return aircraft 10 from storage mode to VTOLflight mode, a reverse sequence may be followed to avoid contact betweenthe various components of aircraft 10 with each other as well as toavoid contact between the various components of aircraft 10 and thesurface on which aircraft 10 rests.

Referring to FIGS. 7A-10D, the chordwise folding operation of a rotorblade is more fully described. The hingeable relationship of rotor blade92 a to rotor hub 94 a is substantially similar to the hingeablerelationship between each rotor blade and the respective rotor hubtherefore, for sake of efficiency, certain features will be disclosedonly with regard to rotor blade 92 a and rotor hub 94 a. One havingordinary skill in the art, however, will fully appreciate anunderstanding of the hingeable relationship between other rotor bladesand rotor hubs based upon the disclosure herein of rotor blade 92 a androtor hub 94 a. In the illustrated portions, rotor hub 94 a includes apitch horn 100, a leading fairing 102 and a trailing fairing 104, asbest see in FIGS. 7A-7B. In addition, rotor hub 94 a includes a gripassembly 106 and a harness 108 that are coupled together with connectors110 a, 110 b along axis 112, as best seen in FIG. 8. It is noted thatthere are two instances of axis 112 labeled in FIG. 8, which symbolizethat the instance of axis 112 extending through grip assembly 106 andthe instance of axis 112 extending through harness 108 are a common axiswhen rotor hub 94 a is fully assembled, wherein harness 108 is at leastpartially disposed within grip assembly 106. It is accordingly to beunderstood by those having ordinary skill in the art that this commonaxis convention will be used throughout FIG. 8.

Rotor blade 92 a is rotatably coupled to grip assembly 106 and harness108 about pivot pin 116 that extends along axis 114. In the illustratedembodiment, spacers 118 a, 118 b are sandwiched between grip assemblyarms 106 a, 106 b and harness 108 along axis 114 and grip assembly arms106 a, 106 b are sandwiched between blade tangs 120 a, 120 b such thatpivot pin 116 passes through blade tang 120 a, grip assembly arm 106 a,spacer 118 a, harness 108, spacer 118 b, grip assembly arm 106 b andblade tang 120 b. A nut 122 is threadably coupled to pivot pin 116 tosecure rotor blade 92 a, grip assembly 106 and harness 108 together.Rotor blade 92 a is secured in the radially extended orientation, asbest seen in FIGS. 7A, 9A and 10A, by a lock assembly depicted asrelease pin 124 that extends along axis 126. In the illustratedembodiment, bushings 128 a, 128 b are sandwiched between grip assemblyarms 106 a, 106 b and harness 108 along axis 126 and grip assembly arms106 a, 106 b are sandwiched between blade tangs 120 a, 120 b such thatrelease pin 124 passes through blade tang 120 a, grip assembly arm 106a, bushing 128 a, harness 108, bushing 128 b, grip assembly arm 106 band blade tang 120 b. A nut 130 is threadably coupled to release pin 124to prevent rotor blade 92 a from rotating relative to grip assembly 106and harness 108 when rotor blade 92 a is in the radially extendedorientation for flight modes of aircraft 10.

A linkage assembly 132 is rotatably coupled to harness 108 and isrotatably coupled to rotor blade 92 a. Linkage assembly 132 includes towlinks 134 a, 134 b, a latch pin 136 and a drag link 138. In theillustrated embodiment, tow links 134 a, 134 b are rotatable about axis126 as tow links 134 a, 134 b are respectively positioned on bearingsurfaces 140 a, 104 b of bushings 128 a, 128 b. Tow links 134 a, 134 brotatably coupled to drag link 138 via latch pin 136 along axis 142.More specifically, tow links 134 a, 134 b are sandwiched between draglink arms 138 a, 138 b with latch pin 136 extending therethrough. Draglink 138 is rotatably coupled to rotor blade 92 a by linkage pin 144. Inthe illustrated embodiment, drag link 138 is sandwiched between spacers148 a, 148 b and between blade tangs 120 a, 120 b such that linkage pin144 passes through blade tang 120 a, spacer 148 a, drag link 138, spacer148 b and blade tang 120 b. A nut 150 is threadably coupled to linkagepin 144 to secure rotor blade 92 a and drag link 138 together. Rotorblade 92 a is secured in the stowed orientation, as best seen in FIGS.7B, 9D and 10D, by a lock assembly depicted as pawl assembly 152. Pawlassembly 152 includes a pawl member 152 a that is coupled to harness 108by pin 154 a in receiving region 156 of harness 108. Pawl assembly 152also includes a pawl member 152 b that is coupled to harness 108 by pin154 b in receiving region 158 of pawl member 152 a and receiving region156 of harness 108.

The operation of chordwise folding and locking of rotor blade 92 a willnow be described. As best seen in FIGS. 9A and 10A, rotor blade 92 a issecured to grip assembly 106 and harness 108 in the radially extendedorientation by pivot pin 116 and release pin 124. This configuration ofrotor blade 92 a relative to grip assembly 106 and harness 108 is usedfor flight modes of tiltrotor aircraft 10. When it is desired to convertaircraft 10 to storage mode, rotor blade 92 a is folded chordwiserelative to grip assembly 106 and harness 108. As a first step, releasepin 124 is removed from its connection with rotor blade 92 a, gripassembly 106 and harness 108, which may be a manual process. In thisconfiguration, rotor blade 92 a is operable to rotate about pivot pin116 relative to grip assembly 106 and harness 108, which may be a manualprocess. As best seen in FIGS. 9B and 10B, rotor blade 92 a has rotatedapproximately 20 degrees relative to grip assembly 106 and harness 108.It is noted that linkage assembly 132 is moving from a contractedorientation to an extended orientation as rotor blade 92 a rotatesrelative to grip assembly 106 and harness 108. The extension of linkageassembly 132 is a result of tow links 134 a, 134 b rotating aboutbearing surfaces 140 a, 104 b of bushings 128 a, 128 b, which remaincoupled to harness 108 without the requirement of release pin 124extending therethrough.

As best seen in FIGS. 9C and 10C, rotor blade 92 a has rotatedapproximately 70 degrees relative to grip assembly 106 and harness 108as linkage assembly 132 continues to be extended between rotor blade 92a and harness 108. In addition, latch pin 136 of linkage assembly 132 isapproaching pawl assembly 152. As best seen in FIGS. 9D and 10D, rotorblade 92 a has rotated approximately 90 degrees relative to gripassembly 106 and harness 108 as linkage assembly 132 continues to beextended between rotor blade 92 a and harness 108. Rotor blade 92 a isnow in the stowed orientation. In addition, latch pin 136 of linkageassembly 132 has engaged pawl assembly 152, which now locks rotor blade92 a in the stowed orientation relative to the harness 108. Morespecifically, as latch pin 136 of linkage assembly 132 engages pawlassembly 152, latch pin 136 passes across pawl member 152 b and enters areceiving region 160 of harness 108. Once latch pin 136 enters region160, pawl member 152 b prevent latch pin 136 from exiting region 160 andthus locks rotor blade 92 a in the stowed orientation relative to theharness 108.

When it is desired to return aircraft 10 to flight mode, rotor blade 92a is unfolded chordwise relative to grip assembly 106 and harness 108.As a first step, pawl member 152 a is depressed to eject latch pin 136from region 160 of harness 108, which may be a manual process. In thisconfiguration, rotor blade 92 a is operable to rotate about pivot pin116 relative to grip assembly 106 and harness 108 such that rotor blade92 a may be returned to the radially extended orientation, which may bea manual process. It is noted that linkage assembly 132 is moving fromthe extended orientation to the contracted orientation as rotor blade 92a rotates relative to grip assembly 106 and harness 108. Once rotorblade 92 a is in the radially extended orientation, release pin 124 maybe reinserted through blade tang 120 a, grip assembly arm 106 a, bushing128 a, harness 108, bushing 128 b, grip assembly arm 106 b and bladetang 120 b. Nut 130 may now be threadably coupled to release pin 124 tosecure rotor blade 92 a in the radially extended orientation for flightmodes of aircraft 10.

Referring to FIGS. 11A-11B in the drawings, a tiltrotor aircraft isschematically illustrated and generally designated 210. Aircraft 210includes a fuselage 212, a wing mount assembly 214 that is rotatablerelative to fuselage 212 and a tail assembly 216 including rotatablymounted tail members 216 a, 216 b having control surfaces operable forhorizontal and/or vertical stabilization during forward flight. A wingmember 218 is supported by wing mount assembly 214 and rotates with wingmount assembly 214 relative to fuselage 212 as discussed herein. Locatedat outboard ends of wing member 218 are propulsion assemblies 220 a, 220b. Propulsion assembly 220 a includes a nacelle depicted as fixed pylon222 a that houses an engine and transmission. In addition, propulsionassembly 220 a includes a mast assembly 224 a that is rotatable relativeto fixed pylon 222 a between a generally horizontal orientation, as bestseen in FIG. 11A, a generally vertical orientation, as best seen in FIG.11B. Propulsion assembly 220 a also includes a proprotor assembly 226 athat is rotatable relative to mast assembly 224 a responsive to torqueand rotational energy provided via a rotor hub assembly and drive systemmechanically coupled to the engine and transmission. Likewise,propulsion assembly 220 b includes a nacelle depicted as fixed pylon 222b that houses an engine and transmission, a mast assembly 224 b that isrotatable relative to fixed pylon 222 b and a proprotor assembly 226 bthat is rotatable relative to mast assembly 224 b responsive to torqueand rotational energy provided via a rotor hub assembly and drive systemmechanically coupled to the engine and transmission.

FIG. 11A illustrates aircraft 210 in airplane or forward flight mode, inwhich proprotor assemblies 226 a, 226 b are rotating in a substantiallyvertical plane to provide a forward thrust enabling wing member 218 toprovide a lifting force responsive to forward airspeed, such thataircraft 210 flies much like a conventional propeller driven aircraft.FIG. 11B illustrates aircraft 210 in helicopter or VTOL flight mode, inwhich proprotor assemblies 226 a, 226 b are rotating in a substantiallyhorizontal plane to provide a lifting thrust, such that aircraft 210flies much like a conventional helicopter. It should be appreciated thataircraft 210 can be operated such that proprotor assemblies 226 a, 226 bare selectively positioned between forward flight mode and VTOL flightmode, which can be referred to as a conversion flight mode.

In the illustrated embodiment, proprotor assemblies 226 a, 226 b eachinclude three twisted rotor blades that are equally spaced apartcircumferentially at approximately 120 degree intervals. It should beunderstood by those having ordinary skill in the art, however, thatproprotor assemblies 226 a, 226 b of the present disclosure could haverotor blades with other designs and other configurations. During flightmodes, proprotor assemblies 226 a, 226 b rotate in opposite directionsto provide torque balancing to aircraft 210. For example, when viewedfrom the front of aircraft 210 in forward flight mode, proprotorassembly 226 a rotates clockwise and proprotor assembly 226 b rotatescounterclockwise. In addition, proprotor assemblies 226 a, 226 b rotate60 degrees out of phase with each other such that rotor blades ofalternating proprotor assemblies 226 a, 226 b sequentially pass wingmember 218 during all modes of operation of aircraft 210. Further, asdiscussed herein, proprotor assemblies 226 a, 226 b are mechanicallycoupled to a common interconnect drive shaft such that proprotorassemblies 226 a, 226 b have matched counter rotation wherein anyrotation of one proprotor assembly 226 a, 226 b results in an equalcounter rotation of the other of proprotor assembly 226 a, 226 b.

Referring next to FIGS. 12A-12F of the drawings, tiltrotor aircraft 210is depicted in various states during a transition between VTOL flightmode and storage mode. Aircraft 210 has a VTOL flight mode, as best seenin FIG. 11B, a forward flight mode, as best seen in FIG. 11A, and astorage mode, as best seen in FIG. 12F. As discussed above, aircraft 210includes fuselage 212 and wing 218 that is rotatably mounted to fuselage212. Wing 218 is reversibly rotatable between a flight orientation thatis generally perpendicular to fuselage 212, as best seen in FIG. 12A,and a stowed orientation that is generally parallel to fuselage 212, asbest seen in FIG. 12F. Pylon assemblies 222 a, 222 b are positionedproximate the outboard ends of wing 218. Mast assemblies 224 a, 224 bare respectively rotatable relative to pylon assemblies 222 a, 222 b.Mast assemblies 224 a, 224 b are reversibly rotatable between agenerally vertical orientation, as best seen in FIG. 12A, and agenerally horizontal orientation, as best seen in FIG. 12F. Proprotorassemblies 226 a, 226 b are respectively rotatable relative to mastassemblies 224 a, 224 b. Proprotor assembly 226 a includes rotor blades228 a, 228 b, 228 c and proprotor assembly 226 b includes rotor blades228 d, 228 e, 228 f Proprotor assemblies 226 a, 226 b each have aradially extended orientation, as best seen in FIG. 12A, and a stowedorientation, as best seen in FIG. 12F. More specifically in the stowedorientation, rotor blades 228 a, 228 b of proprotor assembly 226 a arefolded beamwise to be generally parallel with rotor blade 228 c androtor blades 228 d, 228 e of proprotor assembly 226 b are foldedbeamwise to be generally parallel with rotor blade 228 f. In addition,rotor blades 228 a, 228 b, 228 c of proprotor assembly 226 a have anascending orientation relative to wing 218 and rotor blades 228 d, 228e, 228 f of proprotor assembly 226 b have a descending orientationrelative to wing 218. In the illustrated embodiment, as proprotorassemblies 226 a, 226 b are 60 degrees out of phase, rotor blades 228 a,228 b, 228 c of proprotor assembly 226 a ascend at an angle ofapproximately 30 degrees relative to wing 218 and rotor blades 228 d,228 e, 228 f of proprotor assembly 226 b descend at an angle ofapproximately 30 degrees relative to wing 218.

An example conversion operation of aircraft 210 from VTOL flight mode tostorage mode will now be described. In FIG. 12A, aircraft 210 is bestcharacterized as being in VTOL flight mode. As illustrated, wing 218 isin flight orientation, generally perpendicular to fuselage 212. Mastassemblies 224 a, 224 b are each in a generally vertical orientation.Proprotor assemblies 226 a, 226 b are each in a radially extendedorientation. Tail members 216 a, 216 b are in a dihedral orientation.Rotor blades 228 a, 228 b, 228 c have been collectively operated to havea generally vertical orientation. Rotor blades 228 d, 228 e, 228 f havebeen collectively operated to have a generally vertical orientation. InFIG. 12B, the conversion from VTOL flight mode to storage mode hasbegun. As illustrated, wing 218 remains in flight orientation, generallyperpendicular to fuselage 212. Mast assemblies 224 a, 224 b remain inthe vertical orientation. Tail members 216 a, 216 b have begun to lower.Rotor blades 228 a, 228 b have begun to fold beamwise, while rotor blade228 c remains radially extended. Rotor blades 228 d, 228 e have begun tofold beamwise, while rotor blade 228 f remains radially extended.Proprotor assemblies 226 a, 226 b have counter rotated approximately 30degrees.

In FIG. 12C, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 218 has rotated approximately 30 degreesrelative to fuselage 212. Mast assemblies 224 a, 224 b remain in thevertical orientation. Tail members 216 a, 216 b continue to lower. Rotorblades 228 a, 228 b continue to fold, while rotor blade 228 c remainsradially extended. Rotor blades 228 d, 228 e continue to fold, whilerotor blade 228 f remains radially extended. In FIG. 12D, the conversionfrom VTOL flight mode to storage mode continues. As illustrated, wing218 has rotated approximately 60 degrees relative to fuselage 212. Mastassemblies 224 a, 224 b have rotated approximately 30 degrees from thevertical orientation toward the horizontal orientation. Tail members 216a, 216 b continue to lower. Rotor blades 228 a, 228 b continue to fold,while rotor blade 228 c remains radially extended. Rotor blades 228 d,228 e continue to fold, while rotor blade 228 f remains radiallyextended.

In FIG. 12E, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 218 has rotated approximately 80 degreesrelative to fuselage 212. Mast assemblies 224 a, 224 b have rotatedapproximately 60 degrees from the vertical orientation toward thehorizontal orientation. Tail members 216 a, 216 b continue to lower.Rotor blades 228 a, 228 b are folded, while rotor blade 228 c remainsradially extended. Rotor blades 228 d, 228 e are folded, while rotorblade 228 f remains radially extended. In FIG. 12F, the conversion fromVTOL flight mode to storage mode is complete. As illustrated, wing 218is in stowed orientation, generally parallel to fuselage 212. Mastassemblies 224 a, 224 b are in the horizontal orientation. Tail members216 a, 216 b are fully lowered to the anhedral orientation. Rotor blades228 a, 228 b are in the stowed orientation folded relative to rotorblade 228 c, which remains radially extended. Rotor blades 228 d, 228 eare in the stowed orientation folded relative to rotor blade 228 f,which remains radially extended. In addition, rotor blades 228 a, 228 b,228 c of proprotor assembly 226 a have an ascending orientation relativeto wing 218 and rotor blades 228 d, 228 e, 228 f of proprotor assembly226 b have a descending orientation relative to wing 218.

As illustrated, the storage mode of aircraft 210 depicted and describedwith reference to FIGS. 12A-12F significantly reduces the footprint ofaircraft 210 as compared to the flight modes of aircraft 210. In theillustrated storage mode of aircraft 210, the stowed orientation of therotor blades does not result in an undesirably large moment being placedon the drive systems. To return aircraft 210 from storage mode to VTOLflight mode, a reverse sequence may be followed to avoid contact betweenthe various components of aircraft 210 with each other as well as toavoid contact between the various components of aircraft 210 and thesurface on which aircraft 210 rests.

Referring next to FIGS. 13A-13F of the drawings, tiltrotor aircraft 210is depicted in various states during a transition between VTOL flightmode and storage mode. Aircraft 210 has a VTOL flight mode, as best seenin FIG. 11B, a forward flight mode, as best seen in FIG. 11A, and astorage mode, as best seen in FIG. 13F. As discussed above, aircraft 210includes fuselage 212 and wing 218 that is rotatably mounted to fuselage212. Wing 218 is reversibly rotatable between a flight orientation thatis generally perpendicular to fuselage 212, as best seen in FIG. 13A,and a stowed orientation that is generally parallel to fuselage 212, asbest seen in FIG. 13F. Pylon assemblies 222 a, 222 b are positionedproximate the outboard ends of wing 218. Mast assemblies 224 a, 224 bare respectively rotatable relative to pylon assemblies 222 a, 222 b.Mast assemblies 224 a, 224 b are reversibly rotatable between agenerally vertical orientation, as best seen in FIG. 13A, and agenerally horizontal orientation, as best seen in FIG. 13F. Proprotorassemblies 226 a, 226 b are respectively rotatable relative to mastassemblies 224 a, 224 b. Proprotor assembly 226 a includes rotor blades228 a, 228 b, 228 c and proprotor assembly 226 b includes rotor blades228 d, 228 e, 228 f. Proprotor assemblies 226 a, 226 b each have aradially extended orientation, as best seen in FIG. 13A, and a stowedorientation, as best seen in FIG. 13F. More specifically in the stowedorientation, rotor blade 228 a of proprotor assembly 226 a is foldedbeamwise below wing 218 and generally conforming with pylon assembly 222a. Rotor blades 228 b, 228 c of proprotor assembly 226 a are foldedbeamwise above wing 218 and generally conforming with pylon assembly 222a. Rotor blades 228 d, 228 e of proprotor assembly 226 b are foldedbeamwise to be generally parallel with rotor blade 228 f and rotorblades 228 d, 228 e, 228 f of proprotor assembly 226 b have a descendingorientation relative to wing 218, wherein the descending orientation isan angle of approximately 30 degrees relative to wing 218.

An example conversion operation of aircraft 210 from VTOL flight mode tostorage mode will now be described. In FIG. 13A, aircraft 210 is bestcharacterized as being in VTOL flight mode. As illustrated, wing 218 isin flight orientation, generally perpendicular to fuselage 212. Mastassemblies 224 a, 224 b are each in a generally vertical orientation.Proprotor assemblies 226 a, 226 b are each in a radially extendedorientation. Tail members 216 a, 216 b are in a dihedral orientation.Rotor blades 228 a, 228 b, 228 c have been collectively operated to havea generally horizontal orientation. Rotor blades 228 d, 228 e, 228 fhave been collectively operated to have a generally verticalorientation. In FIG. 13B, the conversion from VTOL flight mode tostorage mode has begun. As illustrated, wing 218 remains in flightorientation, generally perpendicular to fuselage 212. Mast assembly 224a has rotated approximately 30 degrees from the vertical orientationtoward the horizontal orientation. Mast assembly 224 b remains in thevertical orientation. Tail members 216 a, 216 b have begun to lower.Rotor blades 228 a, 228 b have begun to fold beamwise, while rotor blade228 c remains radially extended. Rotor blades 228 d, 228 e have begun tofold beamwise, while rotor blade 228 f remains radially extended.Proprotor assemblies 226 a, 226 b have counter rotated approximately 30degrees.

In FIG. 13C, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 218 remains in flight orientation,generally perpendicular to fuselage 212. Mast assembly 224 a has rotatedapproximately 60 degrees from the vertical orientation toward thehorizontal orientation. Mast assembly 224 b remains in the verticalorientation. Tail members 216 a, 216 b continue to lower. Rotor blades228 a, 228 b continue to fold beamwise, while rotor blade 228 c remainsradially extended until sufficient clearance with wing 218 isestablished allowing rotor blade 228 c to begin beamwise folding. Rotorblade 228 a has cleared pylon assembly 222 a and has sufficient groundclearance to continue folding. Rotor blades 228 d, 228 e continue tofold beamwise, while rotor blade 228 f remains radially extended. InFIG. 13D, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 218 has rotated approximately 45 degreesrelative to fuselage 212. Mast assembly 224 a has rotated approximately90 degrees from the vertical orientation toward the horizontalorientation. Mast assembly 224 b remains in the vertical orientation.Tail members 216 a, 216 b are fully lowered. Rotor blade 228 a is in astowed orientation beneath wing 218 and generally conforming with pylonassembly 222 a. Rotor blades 228 b, 228 c are each in a stowedorientation above wing 218 and generally conforming with pylon assembly222 a. Rotor blades 228 d, 228 e continue to fold, while rotor blade 228f remains radially extended.

In FIG. 13E, the conversion from VTOL flight mode to storage modecontinues. As illustrated, wing 218 has rotated approximately 80 degreesrelative to fuselage 212. Mast assembly 224 a is in the horizontalorientation. Mast assembly 224 b has rotated approximately 60 degreesfrom the vertical orientation toward the horizontal orientation. Tailmembers 216 a, 216 b are fully lowered. Rotor blade 228 a is in a stowedorientation beneath wing 218 and generally conforming with pylonassembly 222 a. Rotor blades 228 b, 228 c are each in a stowedorientation above wing 218 and generally conforming with pylon assembly222 a. Rotor blades 228 d, 228 e are folded, while rotor blade 228 fremains radially extended. In FIG. 13F, the conversion from VTOL flightmode to storage mode is complete. As illustrated, wing 218 is in stowedorientation, generally parallel to fuselage 212. Mast assemblies 224 a,224 b are in the horizontal orientation. Tail members 216 a, 216 b arefully lowered to the anhedral orientation. Rotor blade 228 a is in astowed orientation beneath wing 218 and generally conforming with pylonassembly 222 a. Rotor blades 228 b, 228 c are each in a stowedorientation above wing 218 and generally conforming with pylon assembly222 a. Rotor blades 228 d, 228 e are in the stowed orientation foldedrelative to rotor blade 228 f, which remains radially extended. Inaddition, rotor blades 228 d, 228 e, 228 f of proprotor assembly 226 bhave a descending orientation relative to wing 218.

As illustrated, the storage mode of aircraft 210 depicted and describedwith reference to FIGS. 13A-13F significantly reduces the footprint ofaircraft 210 as compared to the flight modes of aircraft 210. In theillustrated storage mode of aircraft 210, the stowed orientation of therotor blades does not result in an undesirably large moment being placedon the drive systems. To return aircraft 210 from storage mode to VTOLflight mode, a reverse sequence may be followed to avoid contact betweenthe various components of aircraft 210 with each other as well as toavoid contact between the various components of aircraft 210 and thesurface on which aircraft 210 rests.

The foregoing description of embodiments of the disclosure has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosure to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the disclosure. Theembodiments were chosen and described in order to explain the principalsof the disclosure and its practical application to enable one skilled inthe art to utilize the disclosure in various embodiments and withvarious modifications as are suited to the particular use contemplated.Other substitutions, modifications, changes and omissions may be made inthe design, operating conditions and arrangement of the embodimentswithout departing from the scope of the present disclosure. Suchmodifications and combinations of the illustrative embodiments as wellas other embodiments will be apparent to persons skilled in the art uponreference to the description. It is, therefore, intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. A tiltrotor aircraft having a VTOL flight mode, aforward flight mode and a storage mode, the aircraft comprising: afuselage; a wing rotatably mounted to the fuselage and having first andsecond outboard ends, the wing reversibly rotatable between a flightorientation, generally perpendicular to the fuselage, in the flightmodes, and a stowed orientation, generally parallel to the fuselage, inthe storage mode; first and second pylon assemblies respectivelypositioned proximate the first and second outboard ends of the wing;first and second mast assemblies respectively rotatable relative to thefirst and second pylon assemblies, the first and second mast assembliesreversibly rotatable between a generally vertical orientation, in theVTOL flight mode, and a generally horizontal orientation, in the forwardflight mode and the storage mode; and first and second proprotorassemblies respectively rotatable relative to the first and second mastassemblies, the first and second proprotor assemblies each includingfirst, second and third rotor blades and each having a radially extendedorientation, in the flight modes, and a stowed orientation, in thestorage mode, wherein the first rotor blade of the first proprotorassembly is folded beamwise below the wing generally conforming with thefirst pylon assembly, the second and third rotor blades of the firstproprotor assembly are folded beamwise above the wing generallyconforming with the first pylon assembly, the first and second rotorblades of the second proprotor assembly are folded beamwise to begenerally parallel with the third rotor blade of the second proprotorassembly and the rotor blades of the second proprotor assembly have adescending orientation relative to the wing.
 2. The aircraft as recitedin claim 1 further comprising first and second tail members mounted tothe fuselage, the first and second tail members reversibly rotatablebetween a dihedral orientation, in the flight modes, and an anhedralorientation, in the storage mode.
 3. The aircraft as recited in claim 1wherein, in the storage mode, the first proprotor assembly is positionedaft of the second proprotor assembly.
 4. The aircraft as recited inclaim 1 wherein, in the storage mode, the descending orientation of therotor blades of the second proprotor assembly relative to the wingfurther comprises an angle of approximately 30 degrees.
 5. The aircraftas recited in claim 1 wherein the first proprotor assembly rotatesapproximately 60 degrees out of phase with the second proprotorassembly.
 6. The aircraft as recited in claim 1 wherein the first andsecond proprotor assemblies have matched counter rotation.
 7. Theaircraft as recited in claim 1 wherein each of the first and secondproprotor assemblies further comprises a rotor hub and wherein the rotorblades of each proprotor assembly are respectively hingeably coupled tothe rotor hub.
 8. The aircraft as recited in claim 1 wherein each of thefirst and second proprotor assemblies further comprises a plurality ofrotor blade actuators operable to reversibly rotate the respective rotorblades between the radially extended orientation and the stowedorientation.
 9. The aircraft as recited in claim 1 wherein each of thefirst and second mast assemblies further comprises a pitch controlassembly operable to control a collective pitch of the rotor blades ofthe respective proprotor assembly.
 10. The aircraft as recited in claim1 wherein each of the first and second pylon assemblies furthercomprises a conversion actuator operable to reversibly rotate therespective mast assembly between the generally vertical orientation andthe generally horizontal orientation.
 11. A method of converting atiltrotor aircraft from a VTOL flight mode to a storage mode, theaircraft including a fuselage, a wing rotatably mounted to the fuselageand having first and second outboard ends, first and second pylonassemblies respectively positioned proximate the first and secondoutboard ends of the wing, first and second mast assemblies respectivelyrotatable relative to the first and second pylon assemblies and firstand second proprotor assemblies respectively rotatable relative to thefirst and second mast assemblies, the method comprising: rotating thefirst and second mast assemblies from a generally vertical orientationto a generally horizontal orientation; folding a first rotor blade ofthe first proprotor assembly beamwise from a radially extendedorientation to a stowed orientation beneath the wing and generallyconforming with the first pylon assembly; folding second and third rotorblades of the first proprotor assembly beamwise from radially extendedorientations to stowed orientations above the wing and generallyconforming with the first pylon assembly; folding first and second rotorblades of the second proprotor assembly beamwise to be generallyparallel with a third rotor blade of the second proprotor assembly;rotating the wing from a flight orientation, generally perpendicular tothe fuselage, to a stowed orientation, generally parallel to thefuselage; and counter rotating the first and second proprotor assembliessuch that the rotor blades of the second proprotor assembly have adescending orientation relative to the wing.
 12. The method as recitedin claim 11 further comprising rotating first and second tail membersmounted to the fuselage from a dihedral orientation to an anhedralorientation.
 13. The method as recited in claim 11 further comprisingcollectively adjusting a pitch of the rotor blades of each proprotorassembly before the folding steps.
 14. The method as recited in claim 11further comprising feathering the rotor blades of second proprotorassembly before folding the first and second rotor blades of the secondproprotor assembly.
 15. The method as recited in claim 11 wherein thestep of counter rotating the first and second proprotor assembliesfurther comprises counter rotating the first and second proprotorassemblies such that the descending orientation of the rotor blades ofthe second proprotor assembly relative to the wing further comprises anangle of approximately 30 degrees.
 16. The method as recited in claim 11wherein rotating the wing from the flight orientation, generallyperpendicular to the fuselage, to the stowed orientation, generallyparallel to the fuselage further comprises positioning the firstproprotor assembly aft of the second proprotor assembly.
 17. The methodas recited in claim 11 wherein at least a portion of the step of foldingthe first rotor blade of the first proprotor assembly beamwise from theradially extended orientation to the stowed orientation occurs while thefirst mast assemblies is being rotated from the generally verticalorientation to the generally horizontal orientation.
 18. The method asrecited in claim 11 wherein rotating the first mast assembly from thegenerally vertical orientation to the generally horizontal orientationoccurs before rotating the second mast assembly from the generallyvertical orientation to the generally horizontal orientation.
 19. Themethod as recited in claim 11 wherein at least a portion of the step ofrotating the second mast assembly from the generally verticalorientation to the generally horizontal orientation occurs while thewing is being rotated from the flight orientation, generallyperpendicular to the fuselage, to the stowed orientation, generallyparallel to the fuselage.
 20. The method as recited in claim 11 whereinfolding the first and second rotor blades of the second proprotorassembly beamwise to be generally parallel with the respective thirdrotor blade occurs before rotating the second mast assembly from thegenerally vertical orientation to the generally horizontal orientation.